Various apparatuses have been employed in raising and harvesting large quantities of fish. One such apparatus is a fish growing tank. The fish growing tank typically comprises a large round tank, or perhaps a long rectangular tank, which contains a large volume of water for housing the fish and includes a water circulation system to maintain an oxygen supply in the water. To harvest or retrieve fish of a desired size from a fish growing tank, an operator scoops appropriate sized fish from the tank with a fish net. An advantage of using a fish growing tank to raise large quantities of fish is that it is easy to retrieve the fish from the tank. However, such tanks are expensive to clean and maintain and their control systems are subject to mechanical and power failures, which creates the potential for massive loss of fish.
A simple, less expensive, and less risky apparatus for raising and harvesting fish is a fish cage. The fish cage typically comprises a sturdy rectangular cage with mesh walls and a removable lid. The cages are stocked with fish and submerged in a pond, lake, or other similar water channel, connected by a rope typically tied to a dock. Within these cages, fish are allowed to grow while they are fed and raised for sale. An advantage of using fish cages to raise fish is that the cages are not vulnerable to power failures. However, retrieving the fish from these cages can be difficult.
More specifically, in order to allow for easy handling of the cages, their size is limited, which means that many cages are required to raise a substantial volume of fish. A typical cage size is four feet by four feet square. Harvesting fish from even one of these cages often requires a handful of laborers. As a result, the operations of a large scale fishery are rather labor intensive. In addition, the harvesting operation is quite time consuming, as nets are typically used to scoop the fish from the cages, and requires that the fish be removed from the water at least temporarily, which can injure or even kill the fish.
Feeding and treatment of fish within fish cages can create problems. Containing the feed within the cages for a sufficient period of time to ensure complete consumption by the fish can be difficult. For example, when using sinking feed, oftentimes, the fish will not consume all of the feed before the sinking feed "sinks" below the cage out of reach of the fish. In addition, treating the fish in these cages with a medical solution often requires that the entire pond or lake be treated, which can be expensive and wasteful.
Furthermore, with fish growing tanks and fish cages, there is no simple and efficient way to grade large quantities of fish. For example, in order to retrieve only large sized fish from a fish cage, one or more operators are required to raise the fish cage to the surface of the water, while an additional operator, armed with a fish dip net, scoops the larger fish from the cage, returning any small fish inadvertently retrieved back into the cage. Such a task is undesirably time consuming and labor intensive.
Accordingly, a heretofore unaddressed need exists for a simple apparatus and method for raising large quantities of fish wherein the fish can be fed and treated efficiently and from which the fish can be easily graded by size and harvested for sale. It is to such an apparatus and method that the present invention is directed.